feat(payment): add qrDescription/customerID fields, TTL-based QR polling

- CartPaymentRequest gains qrDescription (brandName > hostname > fallback
  text) and customerID (telegram id)
- QrCreateResponse gains qrTTL; polling window now derived from it
  (min 60s) instead of a fixed 3-minute/36-check cap
- PAYMENT_MAX_CHECKS replaced by PAYMENT_MIN_POLL_SECONDS

src/app/config/constants.ts

@@ -1,6 +1,6 @@
 // Payment polling
 export const PAYMENT_POLL_INTERVAL_MS = 5000;
-export const PAYMENT_MAX_CHECKS = 36;
+export const PAYMENT_MIN_POLL_SECONDS = 60;
 export const PAYMENT_TIMEOUT_CLOSE_MS = 3000;
 export const LINK_COPIED_DURATION_MS = 2000;